That doesn't say anything about tank requirements, but it does mention what I said about disease. Seriously, I'm just saying, people already are mislead about goldfish, with the whole "fish in a bowl" concept. So it's better not to throw info out to people that's not entirely accurate.
Hey people if you want nice fish that also do that just get feeder fish. Get a few small ones it is usually cheaper and they are perfect tank-mates for other fish unless you have predatory fish also they live long. I have had mine for 6 years so far.
They are only perfect tank mates for other goldfish, and I should note they need a tank of at least 36 gallons just for themselves, because they get up to 12". You should always quarantine them before putting them with other goldfish - because they often have diseases because they are in cramped spaces with many other fish that aren't well taken care of.
When they are in those conditions they get real hardy over time. But mine live in a pond (50 gallon tank and only 4 fish) (they were supposed to be for my turtle) and they eat almost anything that goes in the water except the guppies and mollies